Ethylene polymerization process

ABSTRACT

A gas phase polymerization of ethylene is disclosed. The process uses a single-site catalyst containing at least one heteroatomic ligand selected from boraaryl, azaborolinyl, pyridinyl, pyrrolyl, indolyl, indenoindolyl, carbazolyl, and quinolinyl. The catalysts are immobilized onto a support. The process comprises polymerizing an ethylene that contains from about 5 to about 15 mole % of a C 3 -C 10  α-olefin and gives polyethylene having a reduced viscosity.

[0001] This is a continuation-in-part of Appl. Ser. No. 09/515,839,filed Feb. 29, 2000.

FIELD OF THE INVENTION

[0002] The invention relates to an ethylene polymerization process. Moreparticularly, the invention relates to a gas phase polymerization ofethylene with a single-site catalyst. The process produces polyethylenehaving a reduced density.

BACKGROUND OF THE INVENTION

[0003] Linear low density polyethylene (LLDPE), which has a density from0.916 to 0.940 g/mL, has penetrated all traditional markets forpolyethylene, including film, molding, pipe, and wire and cable. Due toits strength and toughness, LLDPE has been largely used in the filmmarket, such as produce bags, shopping bags, garbage bags, diaperliners, and stretch wrap. LLDPE has been primarily made withconventional Ziegler catalysts. It is typically produced bycopolymerization of ethylene with a long chain α-olefin such as1-butene, 1-hexene, or 1-octene.

[0004] In the early 1980's, Kaminsky discovered a new class of olefinpolymerization catalysts known as metallocenes (see U.S. Pat. Nos.4,404,344 and 4,431,788). A metallocene catalyst consists of atransition metal compound that has one or more cyclopentadienyl (Cp)ligands. Unlike Ziegler catalysts, metallocene catalysts are usuallysoluble in olefins or polymerization solvents and give homogeneouspolymerization systems. Since these catalysts have a single reactivesite (compared with multiple reactive sites of Ziegler catalysts), theyare also called “single-site” catalysts. Metallocene catalysts are morereactive than conventional Ziegler catalysts, and they produce polymerswith narrower molecular weight distributions. Because single-sitecatalysts enhance incorporation of long chain α-olefin comonomers intopolyethylene, they are of particular interest in the production ofLLDPE.

[0005] Over the last decade, non-metallocene single-site catalysts havealso been developed rapidly. Non-metallocene single-site catalystscontain non-Cp ligands, which are usually heteroatomic ligands, e.g.,boraaryl, azaborolinyl, pyridinyl, pyrrolyl, indolyl, indenoindolyl,carbazolyl, or quinolinyl groups. The development of non-metallocenesingle-site catalysts has provided the polyolefin industry with morechoices of catalysts and opportunities for optimizing the products orproduction processes.

[0006] Non-metallocene single-site catalysts have most of thecharacteristics of metallocene catalysts, including high activity.However, they produce polyethylenes that have relatively high density.For example, boraaryl-based single-site catalysts produce polyethylenesthat have densities from about 0.93 to about 0.97 g/mL (see U.S. Pat.No. 5,554,775). It is of significant interest to further lower thedensity of the polyethylenes produced with non-metallocene single-sitecatalysts.

SUMMARY OF THE INVENTION

[0007] The invention is a gas phase polymerization process for makingethylene polymers, particularly polymers that have reduced densities.The process uses a single-site catalyst containing at least oneheteroatomic ligand selected from boraaryl, azaborolinyl, pyridinyl,pyrrolyl, indolyl, indenoindolyl, carbazolyl, and quinolinyl. Thecatalysts are immobilized onto a support. The process comprisespolymerizing in gas phase an ethylene that contains from about 5 toabout 15 mole % of a C₃-C₁₀ α-olefin in the presence of the supportedcatalyst.

[0008] We have surprisingly found that the gas phase process of theinvention significantly increases the incorporation of α-olefin intopolyethylene and lowers the polyethylene density compared to slurryphase process. Using the gas phase process of the invention, we havesuccessfully prepared ethylene polymers that have densities similar tothose prepared with metallocene single-site catalysts.

DETAILED DESCRIPTION OF THE INVENTION

[0009] The invention is a gas phase polymerization process for preparinga linear low density polyethylene that has a density within the rangefrom about 0.890 to 0.930 g/mL. The process includes supporting asingle-site catalyst. The single-site catalysts suitable for use in theinvention are organometallic compounds having a heteroatomic ligand.Suitable metals are Group 3-10 transition or lanthanide metals.Preferably, the metal is titanium, zirconium, or hafnium. Zirconium isparticularly preferred. Suitable heteroatomic ligands includesubstituted or non-substituted boraaryl, azaborolinyl, pyridinyl,pyrrolyl, indolyl, indenoindolyl, carbazolyl, and quinolinyl, and thelike.

[0010] In addition to a heteroatomic ligand, other ligands are used. Thetotal number of ligands satisfies the valence of the transition metal.The ligands can be bridged or non-bridged. Other suitable ligandsinclude substituted or non-substituted cyclopentadienyls, indenyls,fluorenyls, halides, C₁-C₁₀ alkyls, C₆-C₁₅ aryls, C₇-C₂₀ aralkyls,dialkylamino, siloxy, alkoxy, and the like, and mixtures thereof.Cyclopentadienyls and indenyls are preferred.

[0011] Methods for preparing heteroatomic ligand-containing single-sitecatalysts are available in the literature. For example, U.S. Pat. Nos.5,554,775, 5,539,124, 5,756,611, and 5,637,660, the teachings of whichare herein incorporated by reference, teach how to make single-sitecatalysts that contain boraaryl, pyrrolyl, azaborolinyl, or quinolinylligands. Co-pending Appl. Ser. Nos. 09/417,510 and 09/826,545, theteachings of which are herein incorporated by reference, teaches how toprepare indenoindolyl ligand-containing single-site catalysts.

[0012] The single-site catalyst is immobilized on a support. The supportis preferably a porous material such as inorganic oxides and chlorides,and organic polymer resins. Preferred inorganic oxides include oxides ofGroup 2, 3, 4, 5, 13, or 14 elements. Preferred supports include silica,alumina, silica-aluminas, magnesias, titania, zirconia, magnesiumchloride, and crosslinked polystyrene. Preferably, the support has asurface area in the range of about 10 to about 700 m²/g, a pore volumein the range of about 0.1 to about 4.0 mL/g, an average particle size inthe range of about 10 to about 500 μpm, and an average pore diameter inthe range of about 10 to about 1000 Å. They are preferably modified byheat treatment, chemical modification, or both. For heat treatment, thesupport is preferably heated at a temperature from about 100° C. toabout 800° C. Suitable chemical modifiers include organoaluminum,organosilicon, organomagnesium, and organoboron compounds.

[0013] The single-site catalysts are supported using any knowntechniques. For example, U.S. Pat. Nos. 5,747,404 and 5,744,417, theteachings of which are incorporated herein by reference, teach how tosupport single-site catalysts onto a polysiloxane or a silylaminepolymer. In one suitable method, the single-site catalyst is dissolvedin a solvent and combined with the support. Evaporation of the solventgives a supported catalyst.

[0014] The catalyst is used with an activator. Activators can be eithermixed with single-site catalysts and supported together on a support oradded separately to the polymerization. Suitable activators includealumoxane compounds, alkyl aluminums, alkyl aluminum halides, anioniccompounds of boron or aluminum, trialkylboron and triarylboroncompounds, and the like. Examples are methyl alumoxane, ethyl alumoxane,triethylaluminum, trimethylaluminum, diethylaluminum chloride, lithiumtetrakis(pentafluorophenyl) borate, triphenylcarbeniumtetrakis(pentafluorophenyl) borate, lithium tetrakis(pentafluorophenyl)aluminate, tris(pentafluorophenyl) boron, tris(pentabromophenyl) boron,and the like. Other suitable activators are known, for example, in U.S.Pat. Nos. 5,756,611, 5,064,802, and 5,599,761, and their teachings areincorporated herein by reference.

[0015] Activators are generally used in an amount within the range ofabout 0.01 to about 100,000, preferably from about 0.1 to about 1,000,and most preferably from about 0.5 to about 300, moles per mole of thesingle-site catalyst.

[0016] The process of the invention includes polymerizing ethylene inthe gas phase over the supported catalyst. Methods and apparatus for gasphase polymerization of ethylene with Ziegler catalysts are well known,and they are suitable for use in the process of the invention. Forexample, U.S. Pat. No. 5,859,157, the teachings of which are hereinincorporated by reference, teaches in detail a gas phase polymerizationof ethylene with a Ziegler catalyst.

[0017] In one suitable method, the polymerization is conducted batchwisewhere ethylene is gradually fed into a reactor in which a supportedsingle-site catalyst is dispersed in-situ. In another method, thepolymerization is conducted continuously where both ethylene and adispersed catalyst are continuously fed into a reactor, and polymerproduct is continuously withdrawn from the reactor.

[0018] The supported catalyst is preferably dispersed into a preformedpolyethylene prior to polymerization. The dispersion process ispreferably performed in-situ, i.e., a preformed polyethylene and thesupported catalyst are added into the reactor in which polymerizationtakes place. The preformed polyethylene and the supported catalyst canbe mixed by melting or by dissolving in a hydrocarbon solvent. When asolvent is used, it is removed from the catalyst before polymerizationtakes place. Preformed polyethylene can be prepared by Ziegler orsingle-site catalysts. The ratio of preformed polyethylene/supportedsingle-site catalyst is preferably from about 100/1 to about1,000,000/1.

[0019] The polymerization is preferably conducted under high pressure.The pressure is preferably in the range of about 150 to about 15,000psi, more preferably from about 500 to about 5,000 psi, and mostpreferably from about 1,000 to about 2,000 psi. Generally, the higherthe pressure, the more productive the process. Polymerizationtemperature is preferably within the range from 50° C. to 250° C., morepreferably from 75° C. to 150° C.

[0020] Chain transfer agents such as hydrogen can be used to control themolecular weight of the product. The proportion of hydrogen used can bevaried. For example, if less hydrogen is used, a higher molecular weightpolymer will be produced.

[0021] Ethylene polymers made by the process include polyethylene andcopolymers of ethylene with a C₃-C₁₀ α-olefin. Suitable α-olefinsinclude propylene, 1-butene, 1-hexene, and 1-octene, and the like, andmixture thereof. The molar ratio of ethylene/α-olefin is within therange of about 85/15 to 95/5. The invention produces ethylene polymershaving a density within the range from about 0.890 to about 0.930 g/mL,preferably 0.900 to 0.920 g/mL. The polymers are widely used in theindustry for making polyethylene films, sheets, molded parts, and otherproducts.

[0022] The following examples merely illustrate the invention. Thoseskilled in the art will recognize many variations that are within thespirit of the invention and scope of the claims.

EXAMPLE 1 Gas Phase Polymerization With Quinolinoxy-Based Single-SiteCatalyst

[0023] Preparation Of (8-Quinolinoxy)TiCl₃

[0024] 8-Quinolinol powder (1.45 g, 10 mmol) is added into a flask,stirred, and purged with nitrogen at 25° C. for 10 minutes. Heptane (100mL) is then added into the flask. The reactor contents are stirred at40° C. with nitrogen flow for 20 minutes. Titanium tetrachloride (TiCl4)solution in heptane (10 mL, 1.0 mole/L) is added dropwise into the flaskover 30 minutes. Additional heptane (100 mL) is then added to thereaction mixture and stirred at 25° C. with nitrogen flow for 4 hours.Stirring is discontinued and the reaction mixture is settled overnight.A light-red solid is formed and precipitated from the solution. Thesolid is isolated by decanting the solvents.

[0025] Preparation Of (8-Quinolinoxy)Ti(CH₂-Ph)₃

[0026] Ethylene dichloride (100 mL) is added into the solid preparedabove in a flask. The reactor contents are stirred, and purged withnitrogen at 25° C. for 30 minutes. Benzylmagnesium chloride(Cl-Mg-CH₂-Ph) solution in diethyl ether (1.0 mole/L, 30 mL) is addeddropwise into the flask over 7 hours with stirring at 25° C. The solventis removed by distillation, yielding the catalyst complex(8-Quinolinoxyl)Ti(CH₂-Ph)₃.

[0027] Supporting The Catalyst Onto Silica

[0028] Silica (1.0 g, Silica 948, product of Davison Chemical Company)is modified with hexamethyl disilazane (HMDS), aged for three weeks, andcalcined at 600° C. for 4 hours. Heptane (5 mL), dibutyl magnisium (0.6mmol) and the catalyst (8-quinolinoxyl)Ti(CH₂-Ph)₃ (0.2 mmol) are mixedand added into the treated silica with stirring in a flask at 25° C. for30 minutes, resulting in a purple slurry. The solvent is then removed at43° C. by nitrogen purge and the solid then dried under vacuum for 15minutes, yielding silica-supported (8-quinolinoxyl)Ti(CH₂-Ph)₃ catalyst(1.1 g).

[0029] Gas Phase Polymerization of Ethylene

[0030] The polymerization is conducted in a batch reactor. The supportedcatalyst prepared above (0.6 g), triethylaluminum (TEAL, co-catalyst,2.7 mL, 1.0 mole/L in heptane), and LLDPE (200 g) are charged into atwo-liter stainless steel reactor. The reactor contents are heated to75° C. with agitation for 30 minutes to disperse the catalyst. Thereactor is pressured with ethylene (100 psi), hydrogen (20 psi), andnitrogen (180 psi). 1-Hexene (6 mL) is gradually added into the reactorduring the course of polymerization. The polymerization is carried outat 75° C. for 4 hours, and then terminated by cooling the reactorcontents to 25° C. About 800 grams of polymer is produced, and 200 gramsof it is used for the next batch. The polyethylene of the fourth batchhas a density of 0.918 g/mL.

COMPARATIVE EXAMPLE 2 Slurry Phase Polymerization With QuinolinoxylBased Singe-Site Catalyst

[0031] The procedure of example 1 is repeated but the polymerization isconducted in a slurry phase. The supported catalyst prepared in Example1 (0.6 g), TEAL (2.7 mL,1.0 mole/L in heptane), and isobutane (200 mL)are charged into the reactor. The reactor is pressured with ethylene(100 psi), hydrogen (20 psi), and nitrogen (180 psi). 1-Hexene (6 mL) isgradually added into the reactor during the course of polymerization.The polymerization is carried out at 75° C. for 4 hours. Thepolyethylene has a density of 0.941 g/mL.

EXAMPLE 3 Gas Phase Polymerization With Borabenzene Based Single-SiteCatalyst

[0032] Preparation of Supported Catalyst

[0033] (1-Methylboratabenzene) (cyclopentadienyl) zirconium dichloride(10.4 g) and trityl tetrakis (pentafluorophenyl) borate (40.2 g) aredissolved in dry toluene (314 g). The solution is added dropwise to thesilica (363 g, treated as in Example 1) under nitrogen protection withstirring at 25 C. for one hour. The solvent is removed by nitrogen purgeand then dried under vacuum at 40° C., yielding the supported catalyst(385 g). The supported catalyst is a free-flowing orange-yellow powderwith 2.5% by weight of the borabenzene catalyst complex and 9.7% byweight of borate activator.

[0034] Gas Phase Polymerization

[0035] Polymerization is performed in a 2L stainless steel batchreactor. The supported catalyst prepared above (0.535 g), TEAL (1.5 mL,1.0 mole/L in heptane), and polyethylene (157 g, prepared by slurryphase polymerization, having a density of 0.948 g/mL and recurring unitof 1-hexene 4.3% by weight) are charged into the reactor. The reactorcontents are heated at 82 C. for 30 minutes to disperse the catalyst.The reactor is then pressured with ethylene (194 psi), hydrogen (17 psi)and nitrogen (165 psi). 1-Hexene (45 mL) is gradually added into thereactor during the course of polymerization. The polymerization iscarried out at 82° C. for 4 hours and then terminated by cooling thereaction mixture to 25° C. About 440 grams of polymer is collected whichhas a density of 0.932 g/mL and contains 7.9% by weight of recurringunit of 1-hexene.

COMPARATIVE EXAMPLE 4 Slurry Phase Polymerization With Borabenzene BasedSingle-Site Catalyst

[0036] The procedure of Example 3 is repeated but the polymerization isconducted in a slurry phase in a 1 L stainless steel reactor. Thesupported catalyst prepared in Example 3 (0.268 g), TEAL (0.5 mL,1.0mole/L in heptane), and isobutane (350 mL) are charged into the reactor.The reactor is pressured with ethylene (194 psi), hydrogen (17 psi) andnitrogen (165 psi). 1-Hexene (21 mL) is gradually added into the reactorduring the course of polymerization. The polymerization is carried outat 82° C. for 4 hours. The polyethylene has a density of 0.941 g/mL.

EXAMPLE 5 Gas Phase Polymerization With Indenoindolyl Based Single-SiteCatalyst

[0037] The general procedure of Example 3 is followed.Bis(5,8-dimethyl-5,10-dihydroideno[1,2-b]indolyl)zirconium dichloride(see structure I) is prepared by reacting 0.5 equivalent of zirconiumtetrachloride with 1.0 equivalent of an indenoindolyl monoanion. Themonoanion is generated from 5,8-dimethyl-5,10-dihydroindeno[1,2-b]indoleand 1.1 equivalent of n-butyllithium. The indole compound is prepared bythe method of BUU-Hoi and Xuong (J. Chem. Soc. (1952) 2225) by reactingp-tolylhydrazine with 1-indanone in the presence of sodiumacetate/ethanol, followed by reaction of the secondary amine productwith iodomethane in the presence of a basic catalyst (NaOH or Na2CO3) togive the desired N-methylated product (I).

[0038] Bis(5,8-dimethyl-5,10-dihydroideno[1,2-b]indolyl)zirconiumdichloride is immobilized onto a silica. An ethylene that contains up toabout 15 mole % of 1-butene is polymerized in gas phase in the presenceof the supported catalyst and methalumoxane (MAO) activator. Thepolyethylene produced is expected to have a density within the range ofabout 0.890 to about 0.930 g/mL.

COMPARATIVE EXAMPLE 6 Bulk Polymerization With Indenoindolyl BasedSingle-Site Catalyst

[0039] The general procedure of Example 5 is repeated but thepolymerization is performed in bulk with the non-supportedbis(5,8-dimethyl-5,10-dihydroideno[1,2-b]indolyl)zirconium dichloride.The polyethylene is expected to have a density greater than 0.930 g/mL.

We claim:
 1. A process that comprises polymerizing ethylene containingabout 5 to about 15 mole % of a C₃-C₁₀ α-olefin in gas phase in thepresence of a supported catalyst comprising: (a) an organometalliccompound that contains at least one indenoindolyl ligand; (b) anoptional activator; and (c) a support; wherein the polymer produced hasa density within the range of about 0.890 to about 0.930 g/mL.
 2. Theprocess of claim 1 wherein the polymerization is performed at atemperature within the range of about 50° C. to about 250° C.
 3. Theprocess of claim 1 wherein the C₃-C₁₀ α-olefin is selected from thegroup consisting of propylene, 1-butene, 1-pentene, 1-hexene, 1-octene,and mixtures thereof.
 4. The process of claim 1 wherein the support isselected from the group consisting of inorganic oxides and chlorides,and organic polymer resins.
 5. The process of claim 1 wherein theactivator is selected from the group consisting of alumoxanes, alkylaluminums, alkyl aluminum halides, anionic compounds of boron oraluminum, trialkylboron compounds, and triarylboron compounds.
 6. Theprocess of claim 1 wherein the process is performed at a pressure withinthe range of about 300 psi to about 5,000 psi.
 7. The process of claim 1wherein the polymer produced has a density within the range of about0.900 to about 0.920 g/mL.